1. Field of the Invention
The invention relates to a solid state electrolyte layer and an electrode active material layer in which an increase in resistance due to deterioration of a sulfide solid state electrolyte material is suppressed.
2. Description of the Related Art
With the rapid popularization of information-related devices, communication devices, and so on such as personal computers, video cameras, and portable telephones in recent years, the importance of developing batteries that can be used as power supplies for these devices has grown. Moreover, in the automobile industry and so on, the development of high-output, large-capacity batteries that can be used in electric automobiles or hybrid automobiles is progressing. Among the various types of batteries that currently exist, lithium batteries are the focus of attention due to their high energy density.
An organic electrolyte employing a combustible organic solvent is used in current commercially available lithium batteries, and therefore improvements are required in the manner of attaching safety devices for suppressing temperature increases during short-circuits and structures/material surfaces for preventing short-circuits. In an all solid state lithium battery in which a liquid electrolyte is replaced by a solid state electrolyte to make the battery entirely solid, on the other hand, a combustible organic solvent is not used in the battery, and therefore the safety device can be simplified, leading to a reduction in manufacturing cost and an improvement in productivity.
It is available in the field of all solid state lithium batteries that an improvement in an Li ion conductivity of the all solid state lithium battery can be achieved by employing a sulfide solid state electrolyte material in a solid state electrolyte layer and an electrode active material layer.
Meanwhile, attempts have been made at adding a polymer to the solid state electrolyte layer and the electrode active material layer as a binding material. By adding a polymer, flexibility can be provided in the layer, enabling improvements in workability and moldability. For example, Japanese Patent Application Publication No. 11-086899 (JP-A-11-086899) discloses a solid state electrolyte layer that uses butadiene rubber as a binding material and 0.5 Li2S—0.5 P2S5 as a sulfide solid state electrolyte material. Further, Taro Inada et al., “Silicone as a binder incomposite electrolytes”, Journal of Power Sources 119-121 (2003) 948-950 discloses a solid state electrolyte layer in which styrene-butadiene rubber (SBR), a PO-EO copolymer, or silicone rubber is used as the binding material and Li3PO4—Li2S—SiS2 is used as the sulfide solid state electrolyte material. Furthermore, Taro Inada et al., “Fabrications and properties of composite solid-state electrolytes”, Solid State Ionics 158 (2003) 275-280 discloses a solid state electrolyte layer in which SBR or silicone rubber is used as the binding material and Li3PO4—Li2S—SiS2 is used as the sulfide solid state electrolyte material.
Among sulfide solid state electrolyte materials, a sulfide solid state electrolyte material that contains bridging sulfur exhibits high Li ion conductivity but is also highly reactive, and therefore a sulfide solid state electrolyte material containing bridging sulfur deteriorates when it reacts with a polymer, leading to an increase in battery resistance.